Common Infections May Dull Mind

SAN DIEGO -- Mental sharpness appeared dulled with a history of exposure to five common pathogen, with a possible signal for faster cognitive decline as well, an observational study suggested.

Burden of exposure to Helicobacter pylori, cytomegalovirus, Chlamydia pneumoniae, and herpes simplex 1 and 2 was associated with poorer executive function and language skills among adults 55 and older (P=0.002 and P=0.04, respectively), Clinton Wright, MD, of the University of Miami Health System, and colleagues found.

Infectious burden index based on serum evidence of exposure to those pathogens showed the same direction of association with cognitive decline over 5 years, the group reported here at the International Stroke Conference.

But that association only approached significance for memory after adjustment for baseline performance, demographics, and vascular risk factors (P=0.07).

"We have a cross-sectional association and a hint of something longitudinal but it wasn't quite significant, and that might mean that we need longer follow-up or that there's no association with decline," Wright explained.

The period over which cognitive decline was measured may have been too short to determine an impact on granular measures of cognition other than memory, which is the most prominent form of decline with age, suggested Lee Schwamm, MD, vice-chair of neurology at Massachusetts General Hospital in Boston and a spokesperson for the American Stroke Association.

The analysis included 588 adults (mean age 71) with no prior stroke history in the diverse, community-based Northern Manhattan Study cohort. They underwent cognitive testing at baseline, and 287 had 5-year follow-up testing.

"This adds another piece of evidence to the story that chronic infectious burden is a bad thing," Schwamm told MedPage Today.

Infectious contributors have been sought, and found in some cases, for everything from cancers to Lyme disease to chronic fatigue and autoimmunity.

"There's a general interest in how exposure to infectious agents sets up biology processes we don't entirely understand and leads to organ damage," Wright agreed.

His group previously linked a higher burden of infectious exposures to elevated stroke risk and carotid artery plaque, which is suspected to be due to inflammation and vascular disease processes.

In the current study, "the fact that the association was strongest with executive function at baseline fits a nice biological hypothesis," Schwamm told MedPage Today.

"Because white matter disease and disseminated microvascular disease you think would, for sure, show up in executive function," he explained, noting that the latter is the most distributed across brain areas of all cognitive functions.

Adjustment for vascular risk factors in the current study did little to alter the associations between cognitive performance and infectious exposures.

While the observational findings couldn't determine causality or rule out confounding, there could eventually be applications for the clinic, Wright suggested.

"If we get to the point where enough studies have shown this connection, it may be time to consider a treatment trial" for pathogens determined to be of particular relevance, he suggested. "But that's a long way in future."

The study was funded by the National Institute of Neurological Disorders and Stroke.

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